Download Telescopes [5] Some large ground-based optical telescopes

Telescopes
[5]
Galileo’s telescopes: ~1” in diameter x 24-30” long
• Magnify images Î see details
• Gather light over large surface area Î see fainter objects.
Using a lens (refractor)
[Fig.5.2]
Using a mirror (relector)
[Fig. 5.3]
Some large ground-based optical
telescopes Twin Keck 10m (400”) reflectors
Mauna Kea, 1993
Lick 36” Refractor
1888
Mt. Palomar 200” Reflector
1948
Light-gathering power
∝ (mirror area)
∝ (mirror diameter)2
Technological advances
• Lenses Î mirrors
• Thick mirrors Î thin mirrors Europe’s Very Large
passive Î active support Telescope
• Now working on designs for (Four 8m telescopes)
30m diameter telescopes.
Mirror for Gemini 8m Telescope
1
SOAR: MSU’s New 4m Telescope
Superb image quality.
Superb site in Chile.
Highly competitive
for optical/infrared
observations.
Start
operations in
2004
An International Partnership
•
•
•
SOAR on
Cerro Pachón, Chile
•
MSU
University of North
Carolina
National Optical
Astronomy
Observatories
Brazil
SOAR mirror casting
Corning Glass Works
Seal Fire
Hex Layout
SOAR Turnover
Fixture
Sealed Plano
Sag Fire
Handling For Plano Grind
Blank Ready for R2 Grind
2
Just finished polishing the mirror!
by B.F.Goodrich, in Danbury, CT
Radio telescopes
Angular resolution =
wavelength
mirror diameter
• Radio wavelengths are large Î need
large mirror diameter to see smallangle details.
Array of smaller telescopes
simulates a huge aperture.
• Arecibo, Puerto Rico….
[Fig 5.15]
• 1000 ft. diameter, but same angular
resolution as 0.01 ft optical telescope.
Radio galaxy Cygnus A
3
Telescopes in Space
Atmosphere
blocks light
• Atmosphere blocks
light at many
wavelengths
• Atmospheric
turbulence smears
out images.
Hubble Space Telescope
• 2.4m diameter mirror
• Ultraviolet/optical/infrared
• Above (most of) Earth’s atmosphere
• High angular resolution
• Light not blocked in ultraviolet (or infrared)
• Low earth orbit
• 600 km (370 mile) altitude
• 95 min orbits
• Earth blocks view half of each orbit
• But can be reached by shuttle to install new instruments
• Launched in 1990
• To be replaced by JWST in ~2008
4
Don’t write these all down!
Exploring the Solar System
Information explosion in ~ 1970’s,
due to spaceflight.
Great source of
Solar System info:
Nine Planets website
www.seds.org/billa/tnp/
www.seds.org/billa/tnp/
Partial list of missions
Moon:
1.
Luna 3 (1959)
2.
Ranger (1964-65)
3.
Luna 9 lander (1966)
4.
Apollo moonwalks (1968-1972)
Venus
5.
Mariner 2 (1962)
6.
Venera 7 lander (1970)
7.
Venera 15,16 orbiters (1983)
8.
Magellan orbiter (1991-93)
Mars
9.
Mariner 4 (1964)
10. Mariner 9 orbiter (1971)
11. Viking 1,2 landers (1976-80)
12. Pathfinder rover (1997)
Outer planets
13. Pioneer 10 (1973)
14. Pioneer 11 (1974)
15. Voyager 1 (1979-1980)
16. Voyager 2 (1979-1989)
17. Galileo orbiter/probe (1995)
18. Cassini orbiter/probe (2002-2004)
5
Contents of Solar System
•
•
•
•
Object
Sun
9 planets
Moons
Asteroids
% Total Mass
Sun
Jupiter
Comets
All other planets
Satellites & rings
Asteroids
Cosmic dust
99.8
0.1
0.05
0.04
0.00005
0.000002
0.0000001
• rocky mini-planets
• up to a few 10’s of km dia.
• mostly in orbits bewteen Mars and Jupiter
• Comets
• icy
• spend most of time at fringes of Solar System.
• Dust ( ==> meteorites)
The nine planets
Mercury Venus
Earth
Mars Jupiter Saturn
Uranus
Neptune Pluto
6
The orbits of the planets
• Planets all go around
Sun in same direction
• Except for Pluto,they
are in nearly circular
orbits in thin plane.
• These views look
down on that plane at
45o angle.
Edge-on View
The rotation of the planets
• same sense as orbital motion
except:
• Venus (retrograde, very slowly )
• Uranus, Pluto (tipped on side)
7
Two distinct types of planets
• Terrestial planets
• small, rocky, made of heavy elements: silicon, oxygen,
iron, etc.
Same as the Sun
• Giant (Jovian) planets
• large, primarily gas, ice & liquid: hydrogen & helium.
• and then there’s Pluto…
Planet
5
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
4
3
2
Water = 1
Pluto
Neptune
Uranus
Saturn
Jupiter
Mars
Earth
Venus
Mercury
0
Density
g/cm^3
5.4
5.3
5.5
3.9
1.3
0.7
1.2
1.6
2.1
Terrestial vs. Giant - Size & Density
6
5
4
3
2
1
Pluto
Uranus
Saturn
Jupiter
Mars
Earth
Venus
Mercury
0
Neptune
1
Density (g/cm^3)
Density (g/cm^3)
6
8
Differentiation
• Heavy stuff sinks to center of planets
• Giant planets
• total mass, density Îsmall solid cores
• (~10x mass of Earth).
• Terrestrial planets
• cores contain iron, nickel, etc.
• lighter silicates make up crust.
• This separation must have occurred when planets were
hot & liquid.
Moons & Rings
Planet
Known Moons
Rings?
Mercury
0
Venus
0
Earth
1
Mars
2
Jupiter
16
Yes
Saturn
19
Yes
Uranus
18
Yes
Neptune
8
Yes
Pluto
1
9
Some planets and moons
shown in correct relative sizes
Earth
Venus
Mars
Planets:
orbit around
Sun
Moons:
orbit around
planets
Ganymede
Titan
Io
Moon
Mercury
Callisto
Europa
Triton
Pluto
A look back at the Solar System
The view back from Voyager 1, on its way out of the Solar System.
Mosaic of images taken at a distance of 40 au (4 billion miles) from the Sun. The
Sun is blocked out to make the planets visible. The points marked J, E, V, S, U
and N are at the actual locations of the planets. The
little boxes show blow-ups of each planet image
… the planets are all just little dots.
Note how the planets are in a plane.
EARTH
10
The Earth as a Planet
Material from:
Chapter 7: whole chapter.
Chapter 3: fast skim over sect. 3.2, 3.5, 3.6, 3.7 + box on page 73
Age dating from radioactive rocks [6.3]
• Radioactive decay
• unstable atomic nucleus splits into smaller nuclei (different elements)
• Example: Uranium-238 Î Lead-206 + 4 x Helium-4
• Time for 1/2 of
radioactive nuclei
to decay
Fraction Remaining
• Half-life
Number of half-lives
[Fig 6.11]
• Minerals form with radioactive elements
• decays produce “daughter” nuclei that shouldn’t be in pure mineral.
• Ratio of daughter/parent nuclei shows age since mineral was formed.
• This shows age of Earth, Moon = 4.5 billion years.
11
The Earth’s Atmosphere
• Weighs 13.6 pounds per
square inch
•
10-6 of total mass of Earth.
• 78% nitrogen, 21% oxygen,
+ argon, H2O, CO2, etc.
• Ozone (O3) is critical for life
• blocks Sun’s ultraviolet radiation
• Ozone hole: over Antarctica,
where ozone destroyed by manmade pollutants.
• Where did it come from?
• Formed with rest of Earth?
• Released from interior?
• Dumped onto us by comets?
Life
[Fig 7.11]
[7.4]
• Started in CO2 atmosphere, roughly 4 billion yrs ago.
• Life initially only in sea… converted CO2 to oxygen through
photosynthesis.
• The released oxygen was swallowed up in interactions with
surface material until ~ 2 billion yrs ago.
• After 2 billion yrs ago, oxygen able to build up in atmosphere.
• + geological activity buried much of the free carbon.
• Atmosphere then converted to today’s mix:
78% nitrogen, 21% oxygen, 1% everything else.
• Free oxygen Î ozone
Î protection from ultraviolet lightÎ land animals
12
Seasons [3.2]
• Heating of Earth’s surface determined by flux of sunlight.
•
Flux = incident electromagnetic energy per square meter per second.
•
Think of incoming raindrops.
• Earth’s orbit nearly round
… not a factor.
• But tilt of Earth’s axis
+ conservation of angular momentum
==> much higher flux in one half of year than in other.
SUMMER
WINTER
Global Warming
• Greenhouse Effect
• Incoming sunlight passes
through atmosphere.
• Absorbed by ground.
• Re-emitted as infra-red
radiation.
• CO2 gas causes atmosphere to be opaque to infra-red light.
• Infrared light is trapped, so heats surface.
[Fig 7.14]
• The Problem
• Human activity causing huge rise in CO2, other gases.
• So temperature is going up.
• What will the consequences be????
13
Lots of scientific debate about the details….
Is the CO2 increase really causing
the temperature increase?
• Man-made greenhouse effect is clearly
driving up the temperatures.
• But other gasses have bigger effect per
molecule than does CO2.
CO2 concentration, from Antarctic ice cores.
How hot will it get?
• Predictions uncertain - very
complicated interactions between
atmosphere and ground.
• 3o C (5o F) increase by 2030 is typical
prediction.
For more info:
www.ems.psu.edu/info/explore/
GlobalWarming.html Penn State web site
The Interior of the Earth
[Fig 7.2]
• Crust
•
•
•
•
•
~6 km thick under oceans.
20-70 km thick under continents.
Rocks composed of silicon, oxygen, etc.
0.3% of mass.
Mantle
• Slowly flowing semi-solid rock.
• Core
12,800 km
•
•
•
•
7000 km diameter.
Metallic (iron, nickel, sulfur)
Outer core is liquid.
Inner core probably solid.
14
Plate Tectonics
• Crust split into huge plates drifting
around on top of the mantle.
• Driven by convection (same as
bubbles in boiling water).
• Plates pushed apart in
rift zones
•mid ocean
•also Red Sea +
Great Rift Valley).
• Plates bash together in
subduction zones.
• e.g. “Rim of Fire”
around Pacific
Ocean.
• Also fault zones, where one plate slides alongside another.
[Fig 7.7]
Geological Activity on Earth
• Plate collisions Î big-time wrinkling….
… mountain building (e.g. Himalayas, Andes)
• Volcanoes.
• Magma (molten rock) forced upwards from mantle.
• Along mid-ocean ridges (rift zones).
• Around subduction zones (Rim of Fire)
• Hawaiian Island chain:
. • Crust drifts
past hot spot.
• Unusual.
olde
r
volc
ano
es
Hot Spot
15
Geological Activity elsewhere in the
Solar System [6.3]
• Buckling and twisting of crust
• Mountain building
• Volcanoes
• Caused by hot interiors
• Presently occurring on
•
•
•
•
Earth
Venus
Mars
Several moons of the giant planets
• Formerly occurred on Moon, Mercury (lava flows)
How can we tell when this happened?
Crater formation rate
Impact Craters
4
3
2
1
Time before present (billions of years)
• Earth, moon or other large body runs into lots of small stuff
• Requires intersecting orbits between the two bodies.
• Used to be lots more small bodies on intersecting orbits
• We have already smashed into most of them.
16
Impact Craters
The Earth’s Moon
Mercury
Callisto --- a moon of Jupiter.
Impact Craters on Earth
Known impact craters on Earth
Chicxulub Crater, Yucatan
Gravity gradient map
170 km diameter
65x106 years old.
Wiped out dinosaurs. Mass extinctions.
Closest impact crater: Calvin, MI
8.5 km dia.
450x106 years old
NO PICTURE AVAILABLE
Barringer Meteor Crater, Arizona.
1.2 km diameter, 49,000 years old.
Made by 100,000 ton iron-nickel meteorite
with diameter of ~50 meters.
17
Impact Craters as Clocks
The Moon:
Two types of surfaces…
heavily cratered highlands
and smooth maria.
• Constant rain of meteors
continuously makes craters
• Geologic activity
==> lava flows
==> covers over craters
• So number of craters per unit area proportional to
time span since surface was last covered.
18